Add plugin worker integration tests for erasure coding (#8450)

* test: add plugin worker integration harness

* test: add erasure coding detection integration tests

* test: add erasure coding execution integration tests

* ci: add plugin worker integration workflow

* test: extend fake volume server for vacuum and balance

* test: expand erasure coding detection topologies

* test: add large erasure coding detection topology

* test: add vacuum plugin worker integration tests

* test: add volume balance plugin worker integration tests

* ci: run plugin worker tests per worker

* fixes

* erasure coding: stop after placement failures

* erasure coding: record hasMore when early stopping

* erasure coding: relax large topology expectations

test/plugin_workers/volume_fixtures.go

@@ -0,0 +1,49 @@
+package pluginworkers
+
+import (
+	"fmt"
+	"math/rand"
+	"os"
+	"path/filepath"
+	"testing"
+
+	"github.com/seaweedfs/seaweedfs/weed/storage/types"
+)
+
+// WriteTestVolumeFiles creates a minimal .dat/.idx pair for the given volume.
+func WriteTestVolumeFiles(t *testing.T, baseDir string, volumeID uint32, datSize int) (string, string) {
+	t.Helper()
+
+	if err := os.MkdirAll(baseDir, 0755); err != nil {
+		t.Fatalf("create volume dir: %v", err)
+	}
+
+	datPath := filepath.Join(baseDir, volumeFilename(volumeID, ".dat"))
+	idxPath := filepath.Join(baseDir, volumeFilename(volumeID, ".idx"))
+
+	data := make([]byte, datSize)
+	rng := rand.New(rand.NewSource(99))
+	_, _ = rng.Read(data)
+	if err := os.WriteFile(datPath, data, 0644); err != nil {
+		t.Fatalf("write dat file: %v", err)
+	}
+
+	entry := make([]byte, types.NeedleMapEntrySize)
+	idEnd := types.NeedleIdSize
+	offsetEnd := idEnd + types.OffsetSize
+	sizeEnd := offsetEnd + types.SizeSize
+
+	types.NeedleIdToBytes(entry[:idEnd], types.NeedleId(1))
+	types.OffsetToBytes(entry[idEnd:offsetEnd], types.ToOffset(0))
+	types.SizeToBytes(entry[offsetEnd:sizeEnd], types.Size(datSize))
+
+	if err := os.WriteFile(idxPath, entry, 0644); err != nil {
+		t.Fatalf("write idx file: %v", err)
+	}
+
+	return datPath, idxPath
+}
+
+func volumeFilename(volumeID uint32, ext string) string {
+	return fmt.Sprintf("%d%s", volumeID, ext)
+}